For metal wire rod drawing dies, cemented carbide is commonly used that has high hardness and has excellent abrasion resistance and impact resistance. Cemented carbide is produced by sintering hard particles of tungsten carbide (WC), titanium carbide (TiC), or the like with a binder of an iron group metal such as cobalt (Co or nickel (Ni). The most common cemented carbide is an alloy containing WC as hard particles and Co as a binder, and dies made of a cemented carbide that has the composition are used for metal wire rod drawing.
A die is usually manufactured by undergoing a sizing step of polishing the inner surface of a prepared hole of a new die with the prepared hole formed therein or a used die as a primary material to form a die hole having a predetermined diameter. Today, polishing of the inner surface of a die hole is performed by inserting a polishing needle in the die hole while rotating the die and the polishing needle (e.g., Patent Document 1).